Acoustic time delay system



Patented Apr. `28, 1936 PATENT OFFICE I soous'rro 'rnuE nELsYfsrs'rEM npbert M. M01-rn, mutui-n', n. .mimmto lladio Corporation of America, a corporation of laware Application August 26, 1932, Serial No. 680,495 2 Claims. (Cl. 179-1) v 'I'his invention relates to the art of communication, and more particularly to acoustics. It provides a novel means by which a desired time delay is obtained, in a system comprising a combined acoustical path and. electrical circuit. An object of this invention is toprovide a simple and efficient meansto obtain, within a chamber wherein sounds are produced and reproduced, a` delay in transmission in one program circuit with respect to another or to the original.

Another object of this invention is to produce within aradio ,broadcasting studio a transmission time delay of an uncontrolled program circuit -or the purpose oi' obtaining complete control sist essentially..of

of the electrical circuit before the uncontrolled program enters the transmitting circuit.l

lAnother object of this invention is to obtain by novel meansa time delay within wider limits than was heretofore possible, for compliance with modern high quality requirements of radio broadcasting.

still another object of thisinvention is the independence of the system from the acousticall conditions created by the enclosure withinwhich this invention may be operating.

Another object is to obtain uniform -and identical signal fidelity, regardless of the length oi' the delay paths, within reasonable limits by using uni-directional focusing microphones.

AA feature of'this invention is the arrang ment and combination of a plurality o'f both non# directional microphones unidirectional focusing microphones.

Methods of producing acoustical time delays have been known heretofore. Such devices cona series of enclosed-acoustical paths, transducers. being cumbersome in operation and high in cost. are barred from 'extensive application in modern radio broadcasting. e

The principle upon which this invention is based lies in the arrangement of one or a multiplicity of pick-upy points at unequal distances from the common source oi sound, whichare located at different distances from each other tol produce any'suh time delay as may be desired Ifor artinclal reverberation, echo, automatic gain control and the like. The time delay is obtained over the path 'extending from thessouroe where the sound originates to the point of pick-up, the

path length difference between the two points of pick-up and thesource of sound. `l specific embodiment of the'preseit invenoutgoing radio broadcast4 and nlters. Thesev methods.l

tion as applied to automatic volume control is best described and illustrated by the drawing. indicating a typical soundfproducing chamber comprising a floor I, a raised platform 2, a wall 3, and ceilingl. 'Ihe source of sound is indicated 5 at 5, the control circuit pick-up microphones are indicated at i and 1. These microphones are' electrically connected to an amplifier 8. From the amplifier I the vcontrol circuit then enters the common l,control equipment. The program l0 circuit pick-up is accomplished by locating one or more directional focusing microphones 9 at distances from the source of sound greater than those of the control microphones. The control equipment and associated apparatus may be lo l5 cated in the same room or at a remote point.

A As illustrated and mentioned above, the program pick-up is accomplished by one or more directional microphones located at different distances from the source of sound, and then suflizo' ciently amplliled by the ampliner il. The pro- Bram circuit energy then enters the automatic gain control equipment through the program input. To provide sufncient energy for the control 'input, one or a number of non-directional 25 microphones are located as close to the sotnce of sound as is feasible. The amplined output is made equal to that of the program circuit energy and applied to the control equipment input; both circuits from' the microphones thus enter the 30 automatic gain control unit from which the controlled output is then passed on to any utilization circuit such as the radio broadcasting transmitter. l

Continuous automatic gaincontrol must beief- '35 .i'ected at a `rate of changev which lies below 7audibility. For this reason, all automatic gain control devices include an inertial system which causes control action delay to a oertainextent. In present day practice the action of the iner- 40 tial system, compromising between minimum delay and optimum quality performance, 'ex-s tends over a time period of approximately 1/20tli' of a second.

By means of the present invention the auto- 45 matic gain control receives the same program at. equal volume levels from two or more microphone pick-up points over circuits which are isolated from. each other electrically. -With acoustical paths of unequal lengths between the 50 respective microphone pick-up' points, with re- .delay being the result of the open acoustical ang lprogram circuits. looserl acoustical .so

path is in the program circuit. lt is also desirable to have this acousticai path greater for reasons of orchestral balance. With respect to the automatic gain control, only the time difference exists and not the time relation of either of the circuits to the source of sound. Therefore, the control circuit may be considered to be leading the program. circuit by a considerable time element. This circumstance is utilized to effectively oiset the inertia of the control circuit. A practical system for utilizing the control delay and obtaining a suilicient time coincidence of control action with the uncontrolled program circuit, may be had by providing an acoustical path length difference of approximately feet,v which results in a delay of approximately 1/20th of a. second. `Whenever deslred, this circuit may be reversed; that is, the uncontrolled program circuit l0 is made to lead the controlled circuit, instead of lagging, by changing over the electrical connections, or, in other Words, simply changing the electrical arrangement.

I claim: f

l. An arrangement for obtaining a time delay in an outgoing radio broadcasting program originating in astudic, including the combination of a plurality of non-directional microphones aosaioa located substantially near the source of sound within said studio, a directional focusing microphone having a parabolic shape and located at a higher elevation than said non-directional microphones and at a substantial' distance of approximately fifty feet from said non-directional microphones, means for electrically combining the circuits of said non-directional and directional microphones into a common controlled output.

2. An arrangement for obtaining a time delay in an outgoing radio broadcasting program originating in a studio, including the combination of a plurality of non-directional microphones located substantially near the source of desired sound Within said studio, and at least one directional focusing microphone having a parabolic shape and located at a higher elevation than said non-directional microphones at a substan tial distance of approximately ilty feet, said directional focusing microphone being focussed so as to pick up energy from the source of said desired sound, means for electrically combining the circuits of both the non-directional and da rectional microphones in a common controlled output.

ROBERT M. MORRIS. 

